1. Field of the Invention
The present invention relates to fittings for a port in closed fluid systems for providing access to the port. The invention particularly relates to fittings of the type which permit insertion of a probe into the fluid system while the system remains in its closed state.
2. Description of the Prior Art
Many storage vessels, such as railway tank cars and the like, in addition to being provided with loading and unloading ports, are also provided with one or more access hatches for providing access to the interior of the vessel. Such access may be necessary, for example, to take the temperature of the lading in the vessel, to draw off a sample thereof, and the like. Also, it may be necessary to open the interior of the vessel to atmosphere in connection with unloading of the vessel. This has created difficulties in the past, since the hatches are of relatively large diameter and, while open, permit the entry of foreign matter which may contaminate the contents of the vessel. Furthermore, certain cargoes, such as molasses and corn syrup, e.g., are attractive to insects and, when the hatch is open, bees and other insects may enter the vessel and contaminate the cargo.
In order to alleviate these problems, special access fittings have been provided on vessels which permit access and yet do not require the opening of a large hatch. One such prior fitting is a simple tubular member which communicates with a small opening in the vessel wall and has its distal end closed by a cap. The cap may be removed to permit insertion of a probe, such as a thermometer for taking the temperature of the vessel contents, or a probe for the purpose of drawing off a sample of the cargo. The removal of the cap also opens the interior of the vessel to atmosphere to facilitate in unloading operations. Because the access opening to the tank is very small, the possibility of foreign material and insects entering the tank is reduced substantially, but it is not eliminated.
It is known to provide a screen or mesh over an access opening to prevent ingress of insects. However, this interferes with access to the interior of the vessel for the purposes of insertion of a probe, which would require removal of the screen or piercing it, the latter resulting in destroying the screen's effectiveness and/or allowing broken particles of the screen to fall into the vessel. It is also known to provide access ports or fittings with resilient plugs or seals provided with slits to permit the insertion of probe, while sealing around the probe. But such plugs interfere with communication of the interior of the tank with atmosphere or with external superatmospheric pressure sources for assistance in unloading operations.